Fine-grained optical shuffle interconnect topology migration

ABSTRACT

An optical patch unit is adapted for mounting in or on an optical equipment rack and facilitates a migration from one optical shuffle box or topology to another. The optical patch unit simplifies the replacement of an optical shuffle box, in some cases allowing a phased migration that minimizes system down-time. The optical patch units described herein include passive optical patch panels. Chassis card and optical shuffle connections are terminated at the passive optical patch panel, making it possible to simplify the cabling between the chassis cards and the optical shuffle box. Once installed, chassis card cables do not need to be manipulated at all during subsequent optical shuffle maintenance procedures. Other optical patch units described herein include active optical patch units, which make the migration process less dependent on human intervention and can further reduce system down-time.

TECHNICAL FIELD

The present invention generally relates to optical telecommunicationsystems, and more particularly relates to techniques for managingoptical interconnections between optical equipments.

BACKGROUND

Because telecommunication systems are handling increasing quantities ofdata traffic, optics-based equipment and solutions are gaining momentum.Optical fibers are now commonly used to interconnect systems thatrequire a large network bandwidth over long distances, with a relativelylow cost compared to copper cables. As systems grow and opticalsolutions become more affordable, system designers are also beginning touse optical components and interconnections for short-rangecommunications within systems as well as for long-range connectionsbetween systems.

In large-capacity systems, it is common to use a system design that usesan equipment “chassis” as the form factor. Typically, a certain numberof printed circuit board (PCB) “blades” can be inserted into such achassis, and several such chassis can be installed in a rack, allowingsystem designers to build a scalable system. In order to allow thedifferent blades to communicate with one another, each blade needs to beconnected to a backplane, which is responsible to carry thecommunication signals between the blades.

Typically, a backplane is passive, i.e. does not require any externalelectrical power, and is built in such a way that copper traces can beused to exchange information between the blades. FIG. 1 shows an examplechassis 100, which can support several cards that are interconnectedtogether through the backplane 110. Backplane 110 has several connectors120 for connecting each card to it.

In most systems, the backplane is designed to support a star, adual-star, a dual-dual-star or a fully-connected network topology.Depending on the network topology selected, more or less copper tracesmight be required on the backplane. As the number of traces increase,e.g. in the case of a fully-connected network topology, there is a needto develop a multiple layered backplane to account for all the tracesrequired to interconnect all the blades. The common problems withcopper-based backplane are related to the facts that copper require alot of energy in function of the distance, that it is sensitive tointerference, and that it offers a limited bandwidth capacity, whichmeans that several parallel traces might be required to fulfill thebandwidth requirement. FIGS. 2 and 3 show different interconnecttopologies typically designed in backplanes, namely the dual-dual starttopology and the fully connected network topology, respectively.

To simplify the design of backplanes, system designers are increasinglyconsidering the use of optical interconnects. In fact, optics-basedsolutions offer a much higher bandwidth per trace/interconnect, and arenot sensitive to electro-magnetic interference. Both of these qualitiessimply the development of backplanes. As optical-based technologiesbecome the technology of choice for the future, copper backplanes willbe gradually replaced by optical backplanes.

One example of an optical backplane is illustrated in FIG. 4. Basically,an optical backplane can be seen as a group of optical fiber cablesinterconnected together in order to produce a network topology. In theexample backplane 400 shown in FIG. 4, each of the connectors 410 and420 includes multiple fiber ends, e.g., eight fibers per connector. Inthis configuration, the eight fibers extending from a connector 410 onthe left-hand side of backplane 400 are distributed to the eightconnectors 420 on the right-hand side of backplane 400. Thisconfiguration is typically referred to as an optical shuffle. When suchan optical shuffle is installed on the back of a chassis in order tointerconnect several chassis cards, it is referred to as an opticalbackplane. Note that in a chassis, the co-existence of a copper and anoptical backplane is possible.

One or more optical shuffle can be packaged in a box, typically referredto as an optical shuffle box. An optical shuffle box can be used tointerconnected several components of one or more systems. One differencebetween an optical backplane and an optical shuffle box is that theoptical shuffle is not limited to interconnect the cards of a singlechassis, nor is it limited to the use of backplane connectors, e.g.,blind-mate connectors. One example of an optical shuffle box is shown inFIG. 5, where shuffle box 500 includes a large number of opticalconnectors 510 on both the front and back sides of the shuffle box 500.Once again, each of the optical connectors 510 may terminate severaloptical fibers, such as 24 fibers per connector.

With the continued growth of telecommunications and increasingrequirements for flexibility in terms of interconnection specifications,the option of replacing copper backplanes with optical backplanescontinues to become more attractive. Further, replacing those opticalbackplanes with optical shuffle boxes offers systems designers even morebenefits in terms of scalability and flexibility, especially in terms ofinterconnect technology and ease of deployment.

However, the increasing size and complexity of these systems also tendto make system maintenance and system changes more difficult.Accordingly, improved solutions for optical interconnect systems areneeded.

SUMMARY

There are several problems or areas for possible improvement in themaintenance of optical telecommunications racks. For instance, opticalshuffles, whether used in an optical backplane or an optical shufflebox, are typically passive. This means that they have a staticconfiguration or interconnect topology. An equipment failure or anupgrade/downgrade procedure may require the replacement of an opticalshuffle box, either with an identical unit or with a unit having adifferent interconnect topology and/or support for more connections.This replacement typically requires a large number of connections to bemade by a technician. In the process of disconnecting all of the opticalfiber cables from the cards and re-connecting them to the new opticalshuffle box, several problems, such as misconnections, might occur.

Furthermore, when an optical shuffle box needs to be replaced, all ofthe cables need to be moved to the new optical shuffle box. Thisrequires a complete halt to the system's operation during thereplacement of the optical shuffle box. While the use of a redundantoptical shuffle box may reduce the impact of replacement, thisredundancy results in increased system cost.

Several embodiments of the present invention address one or more ofthese problems. Some of these embodiments include an optical patch unitadapted for mounting in or on an optical equipment rack, the opticalpatch unit facilitating a migration from one optical shuffle box ortopology to another. The optical patch unit simplifies the disconnectingof an old optical shuffle and reconnecting a new one, in some casesallowing a phased migration that minimizes down-time of the optics-basedequipment on the system rack.

The optical patch units described herein can be divided into two maincategories. A first category includes units that can be described aspassive optical patch panels. Chassis card and optical shuffleconnections are terminated at the passive optical patch panel, making itpossible to simplify the cabling between the chassis cards and theoptical shuffle box. Once installed, chassis card cables do not need tobe manipulated at all during subsequent optical shuffle maintenanceprocedures.

A second category of the optical patch units described herein includesunits that can be described as active optical patch units. The activeoptical patch unit simplifies the replacement of one shuffle box withanother, whether or not the shuffle boxes have different opticalinterconnect topologies. In particular, the active optical patch unitmakes the migration process less dependent on human intervention, andcan reduce the down-time for the system.

More particularly, embodiments of the present invention include anoptical patch unit adapted for mounting in or on an optical equipmentrack. This patch unit comprises multiple front-side optical connectorreceptacles arranged on a front side of the optical patch unit, as wellas multiple back-side optical connector receptacles arranged on a backside of the optical patch unit. Each front-side optical connectorreceptacle corresponds to a single one of the back-side opticalconnector receptacles. The optical patch unit further includes multipleoptical interconnections, including an optical interconnection betweeneach front-side optical connector receptacle and its correspondingback-side optical connector receptacle.

In some embodiments, the front-side optical connectors and the back-sideoptical connector receptacles are each organized into two or more ports,each port including at least two of the front-side optical connectors.In some of these and in other embodiments, the optical patch unit is apassive patch panel comprising a single, static optical interconnectionbetween each front-side optical connector receptacle and itscorresponding back-side optical connector receptacle. In some cases, thefront-side and back-side optical connector receptacles accommodate amulti-fiber connector, and each of the optical interconnections is amulti-link optical interconnection.

Embodiments of the invention include those in which the optical patchunit is an active optical patch unit, which includes one or more activeoptical shuffle selector cards. Each active optical shuffle selectorcard includes two or more of the front-side optical connectorreceptacles and a set of alternate front-side optical connectorreceptacles, such that each alternate front-side optical connectorreceptacle corresponds to a single one of the front-side opticalconnector receptacles. The active optical shuffle selector card furtherincludes an optical crossbar array providing a selectable opticalinterconnection from each back-side optical connector receptacle to thecorresponding front-side optical connector receptacle and thecorresponding alternate front-side optical connector receptacle. In someof these embodiments, each front-side and back-side optical connectorreceptacle accommodates a multi-fiber connector, and each of theselectable optical interconnections is a multi-link opticalinterconnection. In some cases, the optical crossbar array is arrangedso that all optical links associated with a given back-side opticalconnector receptacle are simultaneously switched from the correspondingfront-side optical connector to the corresponding alternate front-sideoptical connector receptacle, or vice versa. In other cases the opticalcrossbar array is arranged so that each optical link associated with agiven back-side optical connector receptacle can be individuallyswitched from the corresponding front-side optical connector to thecorresponding alternate front-side optical connector receptacle, or viceversa.

Any of the active optical patch units described above may furthercomprise one or more pass-through optical cards, with each pass-throughoptical card comprising two or more of the front-side optical connectorreceptacles and comprising a single, static optical interconnectionbetween each front-side optical connector receptacle and itscorresponding back-side optical connector receptacle. Either of both ofthese pass-through optical cards and the active optical shuffle selectorcards can be modular units adapted for field installation and removal.

Further embodiments of the invention include optical equipmentassemblies that include one or more of the optical patch unitssummarized above and methods for using these optical patch units.Details of all of these embodiments are given below.

Those skilled in the art will recognize additional features andadvantages upon reading the following detailed description, and uponviewing the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The elements of the drawings are not necessarily to scale relative toeach other. Like reference numerals designate corresponding similarparts. The features of the various illustrated embodiments can becombined unless they exclude each other. Embodiments are depicted in thedrawings and are detailed in the description which follows.

FIG. 1 illustrates an example equipment chassis and its backplane.

FIGS. 2 and 3 illustrate examples of network topologies commonly appliedto backplane designs.

FIG. 4 illustrates an example of an optical shuffle.

FIG. 5 shows an example of an optical shuffle box.

FIG. 6 illustrates the use of an optical shuffle box with two equipmentchassis.

FIG. 7 displays an example of a pigtailed optical shuffle box.

FIG. 8 illustrates a passive optical patch panel.

FIG. 9 shows the use of an optical patch panel with several equipmentchassis and an optical shuffle box.

FIG. 10 illustrates several shuffle boxes having differentinterconnection topologies.

FIG. 11 illustrates a migration between shuffle boxes having differentinterconnection topologies.

FIG. 12 pictures an active optical shuffle selector card.

FIG. 13 illustrates a migration between two optical shuffle boxes usingan active optical patch unit.

FIG. 14 is another example of a migration between two optical shuffleboxes.

FIG. 15 illustrates the use of a passive pass-through optical card in anactive optical patch unit.

DETAILED DESCRIPTION

FIG. 6 provides a conceptual illustration of an equipment rack 600,which includes two chassis 610 and an optical shuffle box 620 locatedbetween them. Each of the chassis 610 includes multiple equipment cards630. Using the shuffle box 620, it is possible to interconnect all thecards 630 together, regardless of which chassis they are in. In thisexample, each card is connected to the optical shuffle box, whichcontains the required interconnect network topology between thedifferent communication links of each card.

While the optical shuffle box provides increased flexibility withrespect to the ability to interconnect equipment cards in rack-mountedchassis, there are still several problems or areas for possibleimprovement in the maintenance of optical telecommunications racks. Forinstance, optical shuffles, whether used in an optical backplane or anoptical shuffle box, are typically passive. This means that they have astatic configuration or interconnect topology.

Another problem is that an equipment failure or an upgrade/downgradeprocedure may require the replacement of an optical shuffle box, eitherwith an identical unit or with a unit having a different interconnecttopology and/or support for more connections. This replacement typicallyrequires a large number of connections to be made by a technician. Inthe process of disconnecting all of the optical fiber cables from thecards and re-connecting them to the new optical shuffle box, severalproblems, such as misconnections, might occur.

Furthermore, when an optical shuffle box needs to be replaced, all ofthe cables need to be moved to the new optical shuffle box. Assumingthat the system does not include an already connected, redundant opticalshuffle box, this requires a complete halt to the system's operationduring the replacement of the optical shuffle box. While the use of aredundant optical shuffle box may reduce the impact of replacement, thisredundancy results in increased system cost. Indeed, assuming that eachredundant optical shuffle box is required to have the same completenetwork topology, extra optical fiber cables will be required to theextra optical shuffle box, which implies extra cable and connector costas well as extra operation and maintenance cost. Still further, extraphysical space, i.e., “footprint,” will be required for supporting aredundant configuration. For example, the minimum footprint required bytwo redundant optical shuffle boxes would be double the size required bya single one.

Another issue with optical shuffle boxes is that they often includefront plate connectors. That design is not optimized for minimizing thefootprint of an optical shuffle box. More particularly, with that typeof design the footprint of the optical shuffle box, i.e. the height andthe depth, is typically dependent on the size and the number ofconnectors required on the front and rear plate of the box.

Several embodiments of the present invention address one or more ofthese problems. Some of these embodiments include an optical patch unitadapted for mounting in or on an optical equipment rack, the opticalpatch unit facilitating a migration from optical shuffle box or topologyto another. The optical patch unit simplifies the disconnecting of anold optical shuffle and reconnecting a new one, in some cases allowing aphased migration that minimizes down-time of the optics-based equipmenton the system rack.

The optical patch units described herein can be divided into two maincategories. A first category includes units that can be described aspassive optical patch panels. As will be shown in further detail below,chassis card and optical shuffle connections are terminated at thepassive optical patch panel, making it possible to simplify the cablingbetween the chassis cards and the optical shuffle box. Once installed,chassis card cables do not need to be manipulated at all during opticalshuffle maintenance procedures, since these cables remain connected tothe patch panel during maintenance or during replacement of an opticalshuffle box and do not have to be moved, replaced or reconnected.Furthermore, the lengths of these cables can be calculated or tailoredfor the exact distance between the cards and the patch panel only, sincethese cables will not be later moved. This further simplifies systemmaintenance and reduces clutter in and around the system.

Likewise, as will be clarified further in the detailed discussion below,the use of a passive optical patch panel also allows the maintenance andreplacement of optical shuffle boxes to be simplified. For instance,because an optical shuffle box is connected directly to the passiveoptical patch panel, rather than to individual equipment cards in one ormore chassis, the optical shuffle box can be connected using cables thatare the optimal length for reaching corresponding connector receptacleson the passive optical patch panel. Ideally, multiple optical fibercables of identical length can be used to interconnect an opticalshuffle box and a patch panel. In the context of migration from oneshuffle box to another, it also becomes possible to simply re-use thesame exact optical fiber cables for connecting to the new opticalshuffle box. It also becomes more practical to use a “pigtailed” opticalshuffle box, where short optical cables with dangling connectors on theends emerge directly from the optical shuffle box without the use ofconnectors installed on a front plate of the shuffle box. With thepigtailed shuffle box, the front-plate footprint of the shuffle box canbe largely independent of the number and size of the opticaladaptors/connectors required to connect the optical shuffle.

A second category of the optical patch units described herein includesunits that can be described as active optical patch units. As will beshown in detail below, the active optical patch unit simplifies thereplacement of one shuffle box with another, whether or not the shuffleboxes have different optical interconnect topologies. In particular, theactive optical patch unit makes the migration process less dependent onhuman intervention, and can reduce the down-time for the system.

In some embodiments, the active optical patch unit includes one orseveral removable active optical shuffle selector cards, which may bebased on an array of 1×2 optical crossbar switches. Equipment cards inone or more chassis are connected to the active optical patch unit viaback-side connector receptacles. Once installed, these connectionstypically do not need to be changed. Each back-side connector is mappedto one of two corresponding front-side connector receptacles, via the1×2 optical switches. One shuffle box is connected to one connectorreceptacle of each of these pairs of front-side connector receptacles.For migration purposes, a second shuffle box is connected to the otherconnector receptacle of each of these pairs. The optical interconnectbetween each back-side connector receptacle and the front side of theactive optical patch unit can be switched from one front-side connectorreceptacle in a pair to another, in an automated or semi-automatedfashion, allowing a rapid transition from one interconnect topology toanother, or from a defective shuffle box to a replacement.

With the flexibility given to the selection of the right optical shufflebox using the concept of the optical shuffle selector card, it becomespossible to carefully plan the migration of individual optical channels,instead of migrating all the channels at one. This fine-grainedselection of optical channels could, for example, allow a few opticalchannels to be migrated to the new interconnect configuration, while theother channels could remain using the old optical shuffle topology. Thisflexibility allows to possibly better managing traffic and avoiding theloss of packets.

Optical Shuffle Topology Migration

In the context of the present application, an optical shuffle is acomponent where multiple optical channels are interconnected in order tocomply with a determined interconnect topology. Each optical channel onan optical shuffle is typically terminated by a connector, such as anMPO or an MTP connector, which are multiple-fiber push-on/pull-offconnector systems typically used for indoor cabling and deviceinterconnections. An optical shuffle box is a box where an opticalshuffle and the connectors for the optical shuffle are all terminated.

The discussion that follows refers to the concept of an optical shuffletopology migration. This reflects the support for migrating from oneoptical shuffle topology to another topology. While this could be doneby simply disconnecting the old optical shuffle, replacing it, andreconnecting the connectors, the apparatus and techniques facilitatebetter strategies, which can simplify maintenance procedures andminimize potential errors due to misconnections. The migration from oneoptical shuffle interconnect topology to another can be due to a systemmaintenance procedure requiring the system to scale up or to scale down.In such a case, the interconnect topology might be required to change.

Pigtailed Optical Shuffle Box

As can be seen in FIG. 5, a conventional optical shuffle box typicallyterminates all the connections directly on the box itself. While thismakes the box and the connectors/adapters very strong and well packaged,the design is very rarely optimized for footprint. Considering that eachoptical fiber has a typical diameter of about 250 micrometers (μm), itis possible to fit 1600 optical fibers within an area of one squarecentimeter. This means that optical shuffles could be expected to bebuilt relatively small in size, with their lower size limits dependingon the connector technology and the interconnect topology used. However,in reality, it is currently only possible to fit between 24 and 72optical fibers in conventional optical MT connector (6.4 mm×2.5 mm). Asa result, an optical shuffle box supporting a very large number ofinterconnections can be extremely large, physically, due to the very lowdensity of optical fibers on the connectors.

One way to minimize the footprint of the front plate of an opticalshuffle box is to focus on the design of the required optical shufflefor the specified network topology, making sure to achieve the lowestfootprint as possible in terms of footprint. This can be done by usingpigtailed connectors instead of terminating the connectors on the frontplate of the optical shuffle box. With this approach, the minimum frontplate footprint of the optical shuffle box is not limited by the size ofthe connectors. Also, this approach eliminates a mated pair ofconnectors at the front plate of the optical shuffle box for eachoptical path—this reduces the insertion loss for the networkinterconnect.

FIG. 7 illustrates this approach conceptually. In FIG. 7, the “box”portion of optical shuffle box 700 has a thin front cross-section 710,since it is not limited by the footprint of front-plate opticalconnectors. Instead, optical cables emerge directly from the front sideof optical shuffle box 700, terminating in connector bundles 720.Connector bundles 720 are pictured in FIG. 7 as tall, thin rectangleswith several smaller rectangles in each. Each of these smallerconnectors corresponds to an optical connector plug, such as an MPO orMPT connector, in some embodiments. These connectors can be connected toseparate cables, in these embodiments, in which case each pigtailcomprises of a bundle of optical cables with several distinct connectorbodies at the end. Alternatively, a pigtail may be terminated in a(usually larger) connector body that houses multiple, e.g., eight MTferrules. With this approach, all of the optical connections for a givenport can be made with a single installation of this larger connectorbody. A mix of these approaches might also be used. Each of thepigtailed connector bundles 720 and/or individual connectors in a givenbundle could have short or long optical cables, which could be optimizedin length to connect directly to another system component, such as anoptical patch panel.

The optical cables emerging from optical shuffle box 700, as well as theinterconnecting optical connections within shuffle box 700, may beconstructed in any of several different ways. For example, the opticalinterconnections within the shuffle box 700 may be optical fibersembedded in FR-4 or other rigid or semi-rigid “board” material, in someembodiments, in which case the optical cables emerging from the opticalshuffle box 700 may be conventional, sheathed, fiber optic bundlesterminated in connectors at the appropriate length. In otherembodiments, either or both of the optical cables outside the box andinside the box may be optical waveguides etched in a laminate material.

Passive Optical Patch Panel

One strategy for simplifying the process of optical shuffle migration,i.e., the replacing of one optical shuffle with another, is to use anoptical patch panel. All of the chassis cards to be interconnected viathe optical shuffle are connected to the optical patch panel, as is theoptical shuffle itself. An example optical patch panel 800 isillustrated in FIG. 8, along with an optical shuffle 710. In FIG. 8,optical shuffle 710 has its pigtails omitted, for clarity.

Optical patch panel 800, which may be adapted for mounting on or in anequipment rack along with one or more equipment chassis and one or moreoptical shuffle boxes, has multiple front-side optical connectorreceptacles 810 on a front side of the optical patch panel. Thesefront-side optical connector receptacles 810 may be organized into twoor more “ports” 820, which are simply groups of connector receptacles(each port comprising eight front-side connector receptacles in FIG. 8),with a port 820 generally corresponding to one or several chassis cards.In a rack having two or more chassis mounted in a stacked configuration,with the individual cards inserted vertically, for instance, aparticular port 820 on the optical patch panel may convenientlycorrespond to the one or several chassis card that are vertically inline with that port when the optical patch panel is installed on therack.

Optical patch panel 800 also includes multiple back-side opticalconnector receptacles arranged on a back side of the optical patch panel800. These back-side optical connector receptacles, which are notvisible in the perspective view of FIG. 8, are similar to the front-sideoptical connector receptacles 810, and are configured to mate withconnectors on optical cables 840, a few of which are also illustrated inFIG. 8. Each front-side optical connector receptacle 810 corresponds toa single one of the back-side optical connector receptacles. Opticalinterconnections (not visible in FIG. 8), run through the optical patchpanel 800, so that there is an optical interconnection between eachfront-side optical connector receptacle 810 and its correspondingback-side optical connector receptacle. Note that the front-sideconnector receptacles 810 and the back-side connector receptacles may bedesigned to accommodate multi-fiber optical connectors, such as MPO orMTP connectors. In this case, the optical interconnection between eachfront-side optical connector receptacle 810 and its correspondingback-side optical connector receptacle is a multi-link opticalinterconnection, i.e., consisting of multiple fibers or other opticalwaveguides.

In some embodiments, each front-side optical connector 810 and itscorresponding back-side optical connector receptacle are part of asingle bulkhead adapter or faceplate adapter. One side may be configuredto accept a male connector body, while the other is configured to accepta female connector body, for example. In some cases, such a bulkheadadapter or faceplate adapter may be essentially hollow in construction,but formed so that optical ferrules in connector bodies inserted intothe faceplate are optically aligned, i.e., with an unobstructed opticalline-of-sight between them. In other cases, a bulkhead adapter orfaceplate adapter may include a waveguide, such as an expanded-beaminterconnection, which is made up of an array of lenses with a largediameter waveguide. The latter approach is less prone to failures thatmight arise, for example, from a speck of dust.

FIG. 9 illustrates an example application of the optical patch paneldescribed above, in a rack of optical equipments. Rack 900 includesthree optical chassis 910, each comprising several chassis cards. Rack900 also has an optical shuffle box 920 installed, as well as an opticalpatch panel 930.

The optical shuffle box 920 is used to establish a desiredinterconnection between the chassis cards in chassis 910.Conventionally, the chassis cards would be connected directly to anoptical shuffle or optical shuffle box. However, as discussed above,changes from optical shuffle to another can be challenging with theconventional approach.

In the system described in FIG. 9, the chassis cards are not connecteddirectly to the optical shuffle box 920, but are instead connected tothe optical patch panel 930. More particularly, in the picturedembodiment the chassis cards are connected to back-side opticalconnector receptacles on the optical patch panel 930, e.g., using fiberoptic cables 935.

The optical shuffle box 920 is connected to front-side opticalconnectors on the optical patch panel 930. These connections may be madewith conventional fiber optic cables, in some embodiments, if theshuffle box 920 is configured with front-panel connector receptacles.Alternatively, these connections may be made with pigtailed connectorsor connector bundles emerging from the shuffle box 920, as discussedabove.

A key advantage of the configuration shown in FIG. 9 is that once thechassis card connections are made, they typically do not need to beremoved, even in the event of a migration from one shuffle to another.Further, the chassis cards are connected on the back of the patch panel,while the optical shuffle is connected to the patch panel on the frontside. With this design, when an optical shuffle needs to be replaced,only the cables between the optical shuffle and the patch panels need tobe reconnected, not the ones between the chassis cards and the patchpanel. This change can be accomplished with a straightforwarddisconnection of the old shuffle box and reconnection of a new one,using only front-side connections. By decoupling the interconnectionfrom the chassis cards to the optical shuffle box with an optical patchpanel, it also becomes possible to pre-install all the optical fibercables between the chassis and the patch panel, independently of thenumber of chassis cards installed, or the topology of the opticalshuffle used.

As mentioned above, the optical patch panel may be used with opticalshuffle boxes having front-panel connector receptacles or havingpigtailed connectors. With the pigtailed optical shuffle box, it ispossible to reduce the vertical footprint required by the opticalshuffle box, since the size of the front plate is not dictated by thephysical size of the connectors, which is typically the determinantfactor. One way to take advantage of the reduced front plate footprintof a pigtailed optical shuffle box is to re-use the saved space withanother optical shuffle. In such a scenario, one optical shuffle couldbe used actively by the system, while the other one is used only in caseof failure of the other, for example.

Passive Optical Shuffle Selection

Several different variants of an optical shuffle box might be availablefor a system. These variants might reflect interconnection topologies ofa different type, or might support a larger or smaller number ofinterconnections for a given topology. FIG. 10 illustrates severalexamples of optical shuffle boxes that support different numbers ofinterconnections. The smallest example shown in FIG. 10 supports fourports, while the largest supports 32. Each shuffle box unit illustratedis paired with an optical patch panel below it; optical connections fromthe shuffle box are made directly to the front of the optical patchpanel as discussed earlier.

Manual Optical Shuffle Topology Migration

It will be appreciated that each of the examples in FIG. 10 is pairedwith a passive optical patch panel that is identical in each of the fourexamples. Migrating a system from one of these shuffle boxes to anotheris simply a matter of disconnecting the old shuffle box from the frontof the passive optical patch panel, inserting a new one, and connectingthe new shuffle box to the front of the passive optical patch panel. Ifthe new shuffle box supports the same number of ports and the chassiscard configuration is unchanged, no further action is required. In asystem upgrade, where additional chassis cards are added so thatadditional ports are needed on the shuffle box, the new chassis cardsare connected to the back of the optical patch panel. In many cases,upgrades in system capacity will not require any changes to be made tothe previous chassis card connections.

Accordingly, choosing from among several variant shuffle box sizes for agiven type of system allows system designers to achieve differentscaling factors in terms of interconnect. The more ports an opticalshuffle contains, the more optical fiber interconnect it will require.

The idea of changing from one optical shuffle box with a certaininterconnection topology to another optical shuffle box with anotherinterconnection topology (including a topology of the same type buthaving a different scale) is referred as an optical shuffle topologymigration. The migration described above may be referred to as a“manual” optical shuffle topology migration, in that human manipulationof the optical connections is required. This is to be contrasted with anelectrically controlled configuration, in which at least part of themigration may be handled with electrically controlled switches.

FIG. 11 illustrates the concept of a manual optical shuffle topologymigration. In FIG. 11, two optical shuffle boxes are present in therack. A first optical shuffle box 1110 supports two ports, and thus hastwo pigtailed bundles of connectors. The second optical shuffle box 1120supports four ports. Assuming that the optical shuffle box on the topinitially has its pigtailed connectors connected to the patch panel1130, a technician could disconnect the pigtailed connectors of the topoptical shuffle 1110 from the optical patch panel 1130, and then connectthe corresponding pigtailed connectors of the optical shuffle box 1120located below the patch panel 1130. In this example, the optical shufflebox on the top has only two connectors, while the optical shuffle box atthe bottom has four connectors. Migrating from an optical shuffle withtwo connectors to another with four connectors typically implies aninterconnection topology change between the connectors.

It will be appreciated that the same procedure could also be used forsimply replacing a faulty optical shuffle box, in which case the opticalshuffle box at the bottom would have exactly the same topology as theone on the top. Later, assuming that the optical shuffle box at thebottom is now the one currently used by the system, another opticalshuffle topology migration could be done in the same manner, with yetanother optical shuffle box inserted into the upper location. The ideais simply to keep alternating between the one on the top and the one atthe bottom for each topology migration.

Active Optical Shuffle Selection

The concept of “active” optical shuffle selection relates to an abilityto select an optical shuffle using active components. Depending on theconfiguration of the active components, one or another optical shufflecould be selected for interconnecting system components.

FIG. 12 illustrates an example of an active optical shuffle selectorcard 1200. An active optical shuffle selector card 1200 typicallycorresponds to a port (i.e., group of optical interconnections). Eachactive optical shuffle selector card 1200 includes first front-sideoptical connector receptacles 810 for the corresponding port, as well asa set of alternate front-side optical connector receptacles 1220 for thecorresponding port. Each alternate front-side optical connectorreceptacle 1220 corresponds to a single one of the front-side opticalconnector receptacles 810. The active optical shuffle selector card 1200further includes back-side optical connector receptacles 830; eachback-side optical connector receptacle 830 corresponds to one of thefirst front-side optical connector receptacles 810 and its correspondingalternate front-side optical connector receptacle 1220. An opticalcrossbar array 1240 provides a selectable optical interconnection fromeach back-side optical connector receptacle 830 to the correspondingfront-side optical connector receptacle 810 and the correspondingalternate front-side optical connector receptacle 1220. Active opticalshuffle selector cards 1200 are modular units adapted for fieldinstallation and removal.

As shown in FIG. 12, an optical crossbar array could be used in order toredirect optical signals from the back of the optical shuffle selectorcard to the front ports of the card. Assuming that the optical crossbarswitch located on the card is an array of 1×2 optical crossbars, thenone port from the back of the card could be selectively switched betweentwo outgoing associated ports. That means that the number of opticalconnections on the front side of the card has to be twice the number ofoptical connections on the back side of the optical shuffle selectorcard. This is the case in the example embodiment of FIG. 12, where thereare two sets of eight connector receptacles on the front side, comparedto one set of eight connector receptacles on the back. It should beappreciated that this concept can be extended to allow a back-side portto be selectively connected to one of three (or more) front-side ports.

The two sets of connectors on the front side of active optical shuffleselector card 1200 can be in turn connected to two different opticalshuffles, which means that the crossbar array 1240 allows the back-sideport to be selectively switched between two different optical shuffles.Several options are possible commercially for building optical crossbar1240. Optical crossbar switches are typically meant for large number ofports, e.g. a 16×16 configuration. By requiring an array of 1×2 opticalcrossbars, the design of the optical crossbar array could become muchsimpler, more scalable and more cost effective.

Multiple active optical shuffle selector cards 1200 can be installed ina simple chassis to create a rack-mountable optical patch unit thatpermits an easy and quick migration from one shuffle box to another. Anexample is shown in FIG. 13, where four active optical shuffle selectorcards 1200 are installed in a chassis 1310 to form an active opticalpatch unit 1300. Also shown in FIG. 13 are a two-port optical shuffle1320 and a four-port optical shuffle 1330.

As shown in FIG. 13, several optical shuffle selector cards can beinserted into a chassis. The idea is to use as many optical shuffleselector cards as required for the envisioned system in terms of opticalinterconnect. Additional optical shuffle selector cards can be insertedas the system grows to support more chassis cards. In this example, eachoptical shuffle selector card 1200 contains an array of 512 1×2 opticalcrossbars or switches. This means that the optical interconnects can beswitched at the granularity of a single fiber or optical link. The 5121×2 switches support up to 64 fibers in each of the eight connectorreceptacles per port. Differently sized optical crossbars can be used tosupport different fiber/connector configurations. These opticalcrossbars can allow switching at the granularity of a single opticallink, or may only allow switching to be performed in groups, in variousembodiments.

Electronically-Assisted Optical Shuffle Topology Migration

The concept of “electronically-assisted” optical shuffle topologymigration refers to the fact that there is no need for manual humanintervention in order to actually switch from one optical shuffle box toanother. Assuming that the two optical shuffle boxes contain a differentinterconnection topology, a topology migration is possible by simplyre-configuring the optical crossbar array of each optical shuffleselector cards in order to perform successfully the migration.

Referring back to FIG. 13, it can be seen that both optical shuffle box1320 and optical shuffle box 1330 can be connected to the same opticalshuffle selector cards, at the same time. In the pictured example, thetwo pigtailed bundles from shuffle box 1320 can be connected to theupper connector receptacles on the first two shuffle selector cards1200, while the four pigtailed bundles from 1330 are connected to thelower connector receptacles on the first four shuffle selector cards1200. Of course, this means that each optical shuffle selector cardrequires twice as many connector receptacles as minimally required by asingle optical shuffle. However, this also means that each selector cardcan selectively connect the back-side connections to the chassis cardsfrom one optical shuffle to the other simply, based on the electronicconfiguration of the active switches in the selector cards 1200.

Again looking at FIG. 13, it should be appreciated that the back of thechassis 1310, where the optical shuffle selector cards are inserted, canbe compared to the passive optical patch panel described earlier. Whilethe connector receptacles at the back of the chassis 1310 are connectedto the chassis cards, the optical shuffle selector cards 1200 areconnected in the chassis 1310. Assuming that the optical crossbar arrayused on the optical shuffle cards 1200 is based on 1×2 opticalcrossbars, then optical waveguides could be directed either towards theports on the top front or the bottom front ports of the cards. In thisscenario, the two optical shuffle boxes could be temporarily connectedto the same optical shuffle selector cards, which become responsible forselecting one or the other optical shuffle box. In this example, anarray of 512 1×2 optical crossbars are built per optical shuffleselector card and a two-port topology is migrated to a four-porttopology (or vice versa).

In FIG. 14, the same concept is applied, except that the optical shuffletopology migration occurs from the four-port topology configuration ofshuffle box 1330 to the eight-port topology configuration of a newlyinstalled shuffle box 1410. The same idea could also be used simply toreplace an optical shuffle by another having the same topology, forexample in case of failure.

Pass-Through Optical Card

A migration from one optical shuffle box to another might be required inorder to replace a faulty or malfunctioning optical shuffle box, inwhich case the existing shuffle box can be replaced by another opticalshuffle box with exactly the same number of ports and the sameinterconnect topology. In the context where a system is required toscale, however, an optical shuffle topology migration is required. Thismeans that the optical shuffle box already installed on the system hasan interconnect topology that is required to be changed, either to scaleup or to scale down. Changing the interconnect topology of an opticalshuffle means that more or fewer ports should be available on the newoptical shuffle box, which also means that the number of the opticalwaveguides available and the number of optical fiber cables required forthe new interconnect topology will be more or fewer, depending whetherthe interconnections require scaling up or down.

Some systems are designed to scale up to a certain limit, e.g., up to apoint where all the slots in one or several chassis are occupied. Thelast step of this up-scaling can allow for certain optimizations usingthe techniques and apparatus described above. For example, in order toscale a system to its capacity limit, several intermediate opticalshuffle migration options might be possible. Assuming that a systemcould be scaled using five possible variants of optical shuffleinterconnect topologies, for example, this means that the system couldstart with the first variant for a small size system, and migrate to thesecond, the third, the fourth and finally the fifth variant, as thesystem is scaling to its maximum capacity. Referring to FIG. 13, forexample, possible variants for shuffle interconnect topologies mightinclude support for two, four, eight, sixteen, and thirty-two ports.

When the system has reached its last stage of possible interconnecttopology, there might be no more need to require an optical shuffleselector card with its optical crossbar array function. In fact, thereis no need for such function since there is only one last possibleinterconnect topology for the last scaling variant. Basically, for thelast incremental upgrade of the interconnect topology, all the newconnections available on the last variant of the optical shuffleinterconnect topology are fixed and will not ever need to be migrated toanother optical shuffle topology. Since the last increment of the systemoptical shuffle topology scalability does not require any opticalshuffle selector cards, pass-through cards can be used instead of activeoptical shuffle selector cards. This solution is less expensive and is apassive solution.

For example, assume that an optical equipment installation isupgradeable in several steps, with the largest scale configurationrequiring a sixteen port shuffle and the second largest configurationrequiring eight ports. FIG. 15 illustrates a possible configuration foran optical patch unit configuration that supports the last upgrademigration.

In the illustrated configuration, active optical patch unit 1300 ispopulated with eight active optical shuffle selector cards 1200 andeight passive pass through cards 1510. For the last migration,sixteen-port shuffle box 1520 is connected to the bottom connectorreceptacles of active shuffle selector cards 1200 and to the connectorreceptacles of pass through cards 1510. As is the case in the exampleconfiguration of FIG. 15, the last stepping increment of an opticalshuffle interconnect topology migration typically requires as manypass-through optical cards 1510 as optical shuffle selector cards.

Fine-Grained Optical Shuffle Topology Migration

Given the electronically-assisted optical shuffle topology migrationdescribed above, it is possible to have two different optical shuffleboxes, with possibly different topologies, connected at the same time tothe same optical shuffle selection cards. Since the array of opticalcrossbars on the optical shuffle selector card can be configured oneoptical crossbar at a time, i.e. at the granularity of a single 1×2optical crossbar, it is possible to strategically plan the migration ofthe optical waveguides between the optical shuffles. By carefullyselecting the timing and the order of the waveguides to be migrated, itbecomes possible to strategically provide minimal service disruption, ifnot to completely avoid it.

For example, assuming that two system components require severalcommunication channels between them, all the communication channelsbetween them can be migrated simultaneously in order to providesynchronous migration of the interconnect topology. Alternatively, itcould be done one channel at a time. Also, in a situation where eachcommunication channel is bi-directional, the optical links forcorresponding transmission and reception channels between the twoassociated system components can be migrated simultaneously.

The several embodiments of the invention described above can provideseveral advantages. For example, with the pigtailed optical shuffle box,the front plate footprint can be independent of the number and size ofthe optical adaptors and/or connectors required to connect the opticalshuffle. The passive optical patch panel described herein simplifies thecabling between chassis cards and an optical shuffle box. Becausechassis card cables are terminated at the passive optical patch panel,these cables do not need to be manipulated between optical shufflemaintenance procedures. The length of the cables can be calculated ortailored for the exact distance between the cards and the patch panelonly, which means that once the cables between the chassis cards and thepatch panel are installed, no more maintenance will be required for thatcabling.

Furthermore, by installing the passive optical patch panel between twooptical shuffle boxes, it is possible to plan to greatly simplify themaintenance and/or replacement of an optical shuffle box. Because systemcomponents, such as chassis cards, only need to connect to the patchpanel with known cable length, optical shuffle boxes can be designed forthe right optical cable length to interconnect to the optical patchpanel. Ideally, multiple optical fiber cables of the same length couldbe used to interconnect an optical shuffle box and a patch panel. In thecontext of migration, it becomes possible to simply re-use the sameoptical fiber cables for connecting to the new optical shuffle box.

The process of migrating from one optical shuffle box to another is alsosimplified, as the migration can be completed by simply disconnectingthe old optical shuffle from the front side of the optical patch unitand connecting the cables to a new optical shuffle. This can be quiteadvantageous in terms of cost, simplicity and reliability.

The active optical patch unit described herein also simplifies themigration process between optical shuffle boxes, and has the furtheradvantage of reducing the down-time of the system, whether or not themigration is to replace a defective shuffle box or to move the system toa new shuffle box having a different interconnect topology. Additionalflexibility is provided to with the active optical shuffle selectorcard, which is based on the use of an optical crossbar array thatprovides a selectable optical interconnection from each back-sideoptical connector receptacle to one of two corresponding front-sideoptical connector receptacles. With the active optical shuffle selectorcard, it becomes possible to plan for the migration of chosen opticalchannels, instead of migrating all the channels at once. Basically, thisfine-grained selection of optical channels could, for example, allow afew optical channels to be migrated to the new interconnectconfiguration, while the other channels could remain using the oldoptical shuffle topology. This flexibility allows to possibly bettermanagement traffic and a minimizing of packet loss.

The modular structure of some embodiments of the active optical patchunit allows the use of passive pass-through cards along with or insteadof active optical shuffle selector cards. These can be much cheaper andcompletely passive solutions.

It should be appreciated that in the preceding discussion, terms such as“first”, “second”, and the like, are used to distinguish variouselements, regions, sections, etc., from one another and are not intendedto imply a particular order or priority, unless the context clearlyindicates otherwise. Like terms refer to like elements throughout thedescription. Likewise, as used herein, the terms “having”, “containing”,“including”, “comprising” and the like are open ended terms thatindicate the presence of stated elements or features, but do notpreclude additional elements or features. The articles “a”, “an” and“the” are intended to include the plural as well as the singular, unlessthe context clearly indicates otherwise. When a process is illustratedor claimed herein, it should be understood that the steps or operationsof that process may be performed in any order unless the context clearlyrequires otherwise. Finally, it is to be understood that the features ofthe various embodiments described herein may be combined with eachother, unless specifically noted otherwise.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat a variety of alternate and/or equivalent implementations may besubstituted for the specific embodiments shown and described withoutdeparting from the scope of the present invention. This application isintended to cover any adaptations or variations of the specificembodiments discussed herein. Therefore, it is intended that thisinvention be limited only by the claims and the equivalents thereof.

What is claimed is:
 1. An optical patch unit adapted for mounting in oron an optical equipment rack, the optical patch unit comprising:multiple front-side optical connector receptacles arranged on a frontside of the optical patch unit; multiple back-side optical connectorreceptacles arranged on a back side of the optical patch unit, whereineach front-side optical connector receptacle corresponds to a single oneof the back-side optical connector receptacles; and multiple opticalinterconnections, including an optical interconnection between eachfront-side optical connector receptacle and its corresponding back-sideoptical connector receptacle wherein the optical patch unit is an activeoptical patch unit comprising one or more active optical shuffleselector cards, each active optical shuffle selector card comprising:two or more of the front-side optical connector receptacles; a set ofalternate front-side optical connector receptacles, each alternatefront-side optical connector receptacle corresponding to a single one ofthe front-side optical connector receptacles; and an optical crossbararray providing a selectable optical interconnection from each back-sideoptical connector receptacle to the corresponding front-side opticalconnector receptacle and the corresponding alternate front-side opticalconnector receptacle.
 2. The optical patch unit of claim 1, wherein thefront-side optical connectors and the back-side optical connectorreceptacles are each organized into two or more ports, each portincluding at least two of the front-side optical connectors.
 3. Theoptical patch unit of claim 1, wherein each front-side optical connectorreceptacle and each back-side optical connector receptacle accommodatesa multi-fiber connector, and wherein each of the opticalinterconnections is a multi-link optical interconnection.
 4. The opticalpatch unit of claim 1, wherein each front-side optical connectorreceptacle and each back-side optical connector receptacle accommodatesa multi-fiber connector, wherein each of the selectable opticalinterconnections is a multi-link optical interconnection, and whereinthe optical crossbar array is arranged so that all optical linksassociated with a given back-side optical connector receptacle aresimultaneously switched from the corresponding front-side opticalconnector receptacle to the corresponding alternate front-side opticalconnector receptacle, or vice versa.
 5. The optical patch unit of claim1, wherein each front-side optical connector receptacle and eachback-side optical connector receptacle accommodates a multi-fiberconnector, wherein each of the selectable optical interconnections is amulti-link optical interconnection, and wherein the optical crossbararray is arranged so that each optical link associated with a givenback-side optical connector receptacle can be individually switched fromthe corresponding front-side optical connector to the correspondingalternate front-side optical connector receptacle, or vice versa.
 6. Theoptical patch unit of claim 1, wherein one or more of the active opticalshuffle selector cards are modular units adapted for field installationand removal.
 7. The optical patch unit of claim 1, further comprisingone or more pass-through optical cards, wherein each pass-throughoptical card comprises two or more of the front-side optical connectorreceptacles and comprises a single, static optical interconnectionbetween each front-side optical connector receptacle and itscorresponding back-side optical connector receptacle.
 8. An opticalequipment assembly, comprising: an optical shuffle unit having multipleoptical connectors organized into two or more ports, the optical shuffleunit further including a plurality of shuffle interconnections among theoptical connectors according to an interconnection topology; a pluralityof optical equipment cards adapted for mounting in an equipment chassis,each of the optical equipment cards corresponding to one of the portsand having one or more optical inputs or optical outputs or both; and anoptical patch unit adapted for mounting in or on an optical equipmentrack, the optical patch unit comprising: multiple front-side opticalconnector receptacles on a front side of the optical equipment rack;multiple back-side optical connector receptacles arranged on a back sideof the optical patch unit, wherein each front-side optical connectorreceptacle corresponds to a single one of the back-side opticalconnector receptacles; and multiple optical interconnections, comprisingan optical interconnection between each front-side optical connectorreceptacle and its corresponding back-side optical connector receptacle;wherein the optical inputs and optical outputs for each opticalequipment card are connected to the back-side optical connectorreceptacles, using optical cables, and wherein the optical connectorsfor each port of the optical shuffle unit are connected to thefront-side optical connector receptacles of the optical patch unit,using optical cables, so that the optical equipment cards areinterconnected according to the interconnection topology defined by theoptical shuffle unit; and wherein the optical patch unit is an activeoptical patch unit comprising one or more active optical shuffleselector cards, each active optical shuffle selector card correspondingto a respective port and each active optical shuffle selector cardcomprising: two or more of the front-side optical connector receptacles;a set of alternate front-side optical connector receptacles, eachalternate front-side optical connector receptacle corresponding to asingle one of the front-side optical connector receptacles; and anoptical crossbar array providing a selectable optical interconnectionfrom each back-side optical connector receptacle for the correspondingport to the corresponding front-side optical connector receptacle andthe corresponding alternate front-side optical connector receptacle. 9.The optical equipment assembly of claim 8, wherein each of thefront-side optical connector receptacles and each of the back-sideoptical connector receptacles accommodates a multi-fiber connector, andwherein each of the optical interconnections is a multi-link opticalinterconnection.
 10. The optical equipment assembly of claim 8, whereineach front-side optical connector receptacle of the active optical patchunit and each back-side optical connector receptacle of the activeoptical patch unit accommodates a multi-fiber connector, wherein each ofthe selectable optical interconnections of the active optical patch unitis a multi-link optical interconnection, and wherein the opticalcrossbar array is arranged so that all optical links associated with agiven back-side optical connector receptacle are simultaneously switchedfrom the corresponding front-side optical connector receptacle to thecorresponding alternate front-side optical connector receptacle, or viceversa.
 11. The optical equipment assembly of claim 8, wherein eachfront-side optical connector receptacle of the active optical patch unitand each back-side optical connector receptacle of the active opticalpatch unit accommodates a multi-fiber connector, wherein each of theselectable optical interconnections of the active optical patch unit isa multi-link optical interconnection, and wherein the optical crossbararray is arranged so that each optical link associated with a givenback-side optical connector receptacle can be individually switched fromthe corresponding front-side optical connector to the correspondingalternate front-side optical connector receptacle, or vice versa. 12.The optical equipment assembly of claim 8, wherein one or more of theactive optical shuffle selector cards are modular units adapted forfield installation and removal.
 13. The optical equipment assembly ofclaim 8, wherein the active optical patch unit further comprises one ormore pass-through optical cards corresponding to respective ports,wherein each pass-through optical card comprises two or more of thefront-side optical connector receptacles for the corresponding port andcomprises a single, static optical interconnection between eachfront-side optical connector receptacle and its corresponding back-sideoptical connector receptacle.
 14. The optical equipment assembly ofclaim 8, wherein the optical connectors for one or more ports of theoptical shuffle unit are each at a first end of a corresponding pigtailoptical cable, and wherein the second end of each pigtail optical cableis permanently affixed to the optical shuffle unit.
 15. A method formigrating an optical equipment assembly from a first interconnectiontopology defined by a first optical shuffle unit to a secondinterconnection topology defined by a second optical shuffle unit, eachof the first and second optical shuffle units having a set of two ormore optical connectors organized into two or more ports, wherein theoptical equipment assembly further includes a plurality of opticalequipment cards adapted for mounting in an equipment chassis with eachof the optical equipment cards corresponding to one of the ports andhaving one or more optical inputs or optical outputs or both, the methodcomprising: disconnecting the first optical shuffle unit from an opticalpatch unit that is adapted for mounting in or on an optical equipmentrack, the optical patch unit having multiple front-side opticalconnector receptacles and multiple back-side optical connectorreceptacles, each front-side optical connector corresponding to aback-side optical connector receptacle, and the optical patch unitfurther having an optical interconnection between each front-sideoptical connector receptacle and its corresponding back-side opticalconnector receptacle, and wherein the optical inputs and optical outputsfor each optical equipment card are connected to the back-side opticalconnectors of the optical patch unit, using optical cables, and whereinthe optical connectors for each port of the first optical shuffle unitare initially connected to the corresponding front-side opticalconnector receptacles, using optical cables, so that the opticalequipment cards are interconnected according to the firstinterconnection topology defined by the first optical shuffle unit; andconnecting the optical connectors for each port of the second opticalshuffle unit to front-side connectors of the optical patch unit; whereinthe optical patch unit is an active optical patch unit comprising one ormore active optical shuffle selector cards corresponding to one or morerespective ports, each active optical shuffle selector card comprisingtwo or more of the front-side optical connector receptacles and a set ofalternate front-side optical connector receptacles, each alternatefront-side optical connector receptacle corresponding to a single one ofthe front-side optical connector receptacles, and an optical crossbararray providing a selectable optical interconnection from each back-sideoptical connector receptacle for the corresponding port to thecorresponding front-side optical connector receptacle and thecorresponding alternate front-side optical connector receptacle, whereinthe method comprises, for each of at least one port of the activeoptical patch unit, connecting the optical connectors for the secondoptical shuffle unit to the alternate front-side optical connectorreceptacles for the corresponding port prior to disconnecting thecorresponding optical connectors for the first optical shuffle unit. 16.The method of claim 15, further comprising switching the selectableoptical interconnection for each back-side optical connector receptacleof the at least one port to the corresponding alternate front-sideoptical connector receptacle prior to disconnecting the correspondingoptical connector for the first optical shuffle unit.
 17. The method ofclaim 16, wherein each front-side optical connector receptacle of theactive optical patch unit and each back-side optical connectorreceptacle of the active optical patch unit accommodates a multi-fiberconnector and wherein each of the selectable optical interconnections ofthe active optical patch unit is a multi-link optical interconnection,and wherein the optical crossbar array is arranged so that each opticallink associated with a given back-side optical connector receptacle canbe individually switched from the corresponding front-side opticalconnector receptacle to the corresponding alternate front-side opticalconnector receptacle, or vice versa, the method further comprisingindividually switching every optical link for each back-side opticalconnector receptacle of the at least one port to the correspondingalternate front-side optical connector receptacle prior to disconnectingthe corresponding optical connector for the first optical shuffle unit.18. The method of claim 15, wherein the active optical patch unitfurther comprises one or more pass-through optical cards correspondingto respective ports, wherein each pass-through optical card comprisesthe plurality of front-side optical connector receptacles for thecorresponding port and comprises a single, static opticalinterconnection between each front-side optical connector receptacle andits corresponding back-side optical connector receptacle, the methodfurther comprising connecting optical connectors for the second shuffleunit to the front-side optical connector receptacles of thecorresponding port of each pass-through optical card.